1. Field of the Invention
The present invention relates to an imaging apparatus capable of performing focus detection by a contrast system and a focus control method for the imaging apparatus.
2. Description of the Related Art
In recent digital cameras, some digital cameras have been provided with a focus detection device using contrast detection system. The focus detection device detects a focusing state of an object image based on a difference (contrast) in high frequency components contained in an imaging signal acquired by an image sensor. In the contrast detection system, the high frequency components are extracted from a video signal generated based on the signal from the image sensor. The level of the high frequency components is observed in predetermined sampling intervals. Then, a focus adjustment lens is driven in a direction the level of the high frequency components approaches a peak. Hereinafter, the system is referred to as a contrast automatic focus (AF) system. According to the system, when the level of the high frequency components reaches a predetermined peak range, it can be finally determined that the camera is in an in-focus state.
In the contrast AF system, the in-focus determination is performed using the video signal obtained based on the output signal from the image sensor that captures the image of the object. Accordingly, it is possible to obtain the highly accurate in-focus state as to the object.
Japanese Patent Application Laid-Open No. 2003-295047 proposes a lens-exchangeable imaging apparatus that can perform more high-speed and accurate focus control.
However, the position (in-focus position) at the peak obtained according to the contrast AF system does not always correspond to a focal plane intended by the photographer. For example, when an eye that has a contrast is shot, the photographer may want to focus on eyelashes. In such a case, when the contrast AF system is performed, the eye that has high contrast is detected. Accordingly, it is not possible to set the focal plane to the eyelashes. To solve the problem, after the AF operation, the photographer has to operate an operation member of the lens so that the lens is set to the desired focal plane.